Electroconductive layers for use in electrographic and electrophotographic recording elements

ABSTRACT

AN ELECTROCONDUCTIVE POLYMERIC FILM USEFUL IN CERTAIN RECORDING ELEMENTS, ESPECIALLY ELECTROGRAPHIC RECORDING ELEMENTS INCLUDING A PHOTOCONDUCTIVE LAYER OR OTHER ELECTROSTATIC CHARGE RETAINING LAYER IN ELECTRICAL CONTACT WITH SUCH FILM, IS COMPOSED OF RANDOMLY DISTRIBUTED RECURRING UNITS HAVING THE FOLLOWING FORMULAE:   -(CH(-CH2-R(+))-CH2-O)- X(-) (A) -(CH(-CH2-CL)-CH2-O)- (B)   WHEREIN UNITS (A) CONSTITUTE BETWEEN ABOUT 25-95 MOLE PERCENT OF THE TOTAL AMOUNT OF SUCH RECURRING UNITS IN THE POLYMER, R IS A QUATERNARY AMMONIUM, PHOSPHONIUM, OR TERTIARY SULFONIUM GROUP AND X IS AN ANION.

United States Patent Int. Cl. G03g 5/00 US. Cl. 96--1.5 8 Claims ABSTRACT OF THE DISCLOSURE An electroconductive polymeric film useful in certain recording elements, especially electrographic recording elements including a photoconductive layer or other electrostatic charge retaining layer in electrical contact with such film, is composed of randomly distributed recurring units having the following formulae:

r J r J in 1 n wherein units (A) constitute between about 25-95 mole percent of the total amount of such recurring units in the polymer, R is a quaternary ammonium, phosphonium, or tertiary sulfonium group and X is an anion.

The invention relates to electroconductive layers for use in electrographic and electrophotographic recording elements.

Normally the support used in electrographic and electrophotographic recording elements is conductive or is coated with a conductive layer, and as such plays a role in the formation of the image or record. In an electrophotographic recording element a photoconductive layer stands in contact with an electroconductive layer or sheet, the later being present for carrying off the electrostatic charges at the areas of the photoconductive layer undergoing an exposure to light rays.

In electrographic materials comprising an insulating layer whereon an electrostatic charge pattern is built up by image-wise or record-wise charging e.g. by means of a modulated electron beam, the conductive element (support or layer) serves to apply a voltage thereon, which e.g. in thermoplastic recording takes part in the formation of a ripple image in correspondence with the electrostatic charge pattern applied to an insulating top layer.

Depending on the type of recording and recording material the conductive element should have a conductivity higher than that of the recording element. Preferably the conductivity of the conductive element is at least a factor 10 higher than the conductivity of the recording element. Normally in practice the surface resistivity of the conductive element should not be higher than 10' ohm per sq.cm. at 15% relative humidity.

In the following description the term electrographic recording is intended so as to include electrographic recording methods and materials as well as the electrophotographic recording methods and materials.

A class of electroconductive polymeric materials has been discovered which is particularly useful for forming an electroconductive layer in an electrographic recording element.

According to the invention an electrographic recording element is provided, comprising a support and a photoconductive layer or an insulating layer which stands in electrical contact with a sheet or layer containing or consisting ofa n electroconductive polymeric material composed of randomly distributed units of the formulae:

lie J -J it? J wherein the ratio of units (A) is between 25 and mole percent of the total and wherein R stands for an onium group and X for an anion.

The R-groups include quaternary ammonium or phosphonium groups or ternary sulphonium groups. Examples of R are trialkyl-ammonium, tri(hydroxyalkyl)-ammonium, N-alkyl-di(hydroxyalkyl)-ammonium, alicyclic ammonium, triarylammoriium, N-dialkyl-aralkylammonium, heterocyclic ammonium, trialkylphosphonium, triarylphosphonium, dialkylsulphonium, S-alky1hydroxy-alkylsulphonium, di(hydroxyalkyl) sul'phonium, S alkyl-carboXyalkyl-sulp-honium, S-alkyl-carboxyalkoxyalkylsulphonium, diaryl-sulphonium, s-alkyl aralkylsulphonium and di(alkoxyalkyl)-sulphonium. In these onium compounds the different alkyl groups may be branched or straight alkyl groups of 1 to 4 carbon atoms.

Examples of X are halide, methylsulphate, polysulphonate or a per-cholrate ion.

More specific examples of the R+X- salt groups are pyridinium chloride, quinolinium chloride, N-methylmorpholinium methylsulphate, N-methylpyridinium methylsulphate, N-methyl-di(hydroxyethyl) ammonium chloride, N-ethyl-di(hydroxyethyD-ammonium chloride, tri- (hydroxyethyD-ammonium chloride, triphenylphosphonium chloride, tributylphosphonium chloride, and methyl hydroxyethylsulphonium methylsulphate.

The electroconductive polymeric materials according to the invention may be prepared according to different reaction methods. In a first reaction method polyepichlorohydrin is used a a quaternizing agent for tertiary amine, a tertiary phosphine or a secondary sulphide. The electroconductive polymers can also be prepared by reaction of polyepichlorohydrin with a secondary amine, e.g., morpholine, or with a mercaptan such as Z-mercaptoethanol followed by quaternization of the obtained product with alkylating agents such as the esters of an alcohol and a strong acid such as methyl or ethyl esters of sulphuric acid, phosphoric acid, hydrochloric acid, hydrobromic acid or hydroiodic acid, e.g. dimethyl sulphate or bromoethanol.

In these reactions the molecular weight of the polyepichlorohydrin may vary within wide limits. The commercially available epichlorohydrins generally possess a rather low molecular weight beneath 3000. However, poly epichlorohydrins having a molecular weight of approximately 70,000 have been described in J. Polymer Sci. 40 (1959) p. 5 71. These high molecular weight polyepichlorohydrins can also be converted according to the above reaction method into quaternized electroconductive polymeric materials.

In these reactions a part of the recurring units of the polyepichlorohydrin is converted into units comprising quaternary ammonium or phosphonium salt groups or ternary sulphonium salt groups. The higher the number of quaternized recurring units, the higher is the electroconductivity of the polymer. It has been found that a sulficient conductivity could be attained if at least 25 mole percent of the recurring units have been converted. The relative humidity must of course be taken into account as will be explained further on. The highest conversion coefficient f d was approximatively 95 mole percent. Beyond this value no substantial improvement of the conductivity could be observed anymore.

These electroconductive polymers are soluble in water. Their electroconductivity is determined by a measurement of their surface resistance. Therefore, a 10% aqueous solution of the polymer is applied to a glass plate. The resulting layer is dried and conditioned at a specific relative humidity. The surface resistance measurements are performed by means of a cell, both poles of which have a width of 0.5 cm. and are at a distance of 1 cm. from each other. In order that the layer should have a sufiicient conductivity and that it could be used as an electroconductive layer in an electrographic recording element, the surface resistance should not exceed well defined limits, which themselves are influenced by the relative humidity degree. For example, the surface resistance at 20% relative humidity should not be higher than 10 ohm/sq. 0111., whereas at 75% relative humidity it should be lower than 10' ohm/sq. cm.

Layers of the electroconductive polymeric materials can be applied by spray, brush, roller, doctor blade, air brush, or wiping techniques to different kinds of supports, e.g.

.paper. Films of synthetic polymers such as cellulose acetate, polystyrene, polyester, polycarbonate, can also be coated with the electroconductive layers. If necessary, these film supports can be provided previously with a known subbing layer whereon the electroconductive layer is coated afterwards.

The amount of applied electroconductive polymeric material of course depends on the support used. When this support is made of paper and especially from a highly porous paper stock, more electroconductive polymeric material will have to be applied than in the case of a nonporous synthetic support, e.g., of polyester. There can be said, however, that in general an amount of 0.5 to 5 g./ sq. m. amply sufiices to provide the layer with a good conductivity.

When paper is used as the support, the electroconductive polymeric materials will also impart electroconductivity when the paper base is thoroughly soaked with an aqueous solution of the electroconductive polymeric materials of the invention. After drying the thus impregnated paper, the electroconduutive polymeric material remains dispersed throughout the entire paper base. Electroconductivity may also be conferred to the paper base by adding a sufficient quantity of an aqueous solution of the electroconductive polymeric materials to the papermaking pulp. The amount of incorporated conductive polymer is determined by the required degree of conductivity.

In addition to the electroconductive polymer the composition of the electroconductive layer may include stabilizing agents against migrating forces, plasticizers, dispersing agents, pigments, and binders, such as gelatin.

A series of preparations of the electroconductive polymers according to the invention is given hereinafter.

PREPARATION 1 Quaternization of pyridine 4 The polymer contained approximately 55 mole percent of modified (A) units.

PREPARATION 2 Quaternization of triethanolamine 15.7 g. of polyepichlorohydrin having a molecular weight of 450 and 13 g. of triethanolamine were heated for 24 h. to 135 C. on an oil-bath. The rest of the preparation 2 is analogous to that of Preparation 1. The resulting polymer contained mole percent of randomly distributed recurring units of the formula:

PREPARATION 3 Quaternization of N-ethyl-diethanolamine 30 g. of polyepichlorohydrin having a molecular weight of 1000 and 21.3 g. N-ethyl-diethanolamine were heated for 48 hours to 135 C. on an oil-bath. Of the recurring units of the polyepichlorohydrin 35 mole percent were modified into the following unit:

' CHCH2 O CE; in 101- 0mm...

CH CH C 3 OH OH PREPARATION 4 Quaternization of morpholine (a) 11.5 g. of polyepichlorohydrin having a molecular weight of 1150 and 20.9 g. of morpholine were heated to 9 hours at C. Acetone was added to the reaction mixture in order to precipitate the morpholinium chloride formed, which precipitate was sucked off, and washed with acetone and ether, whereafter the filtrate was dried by evaporation. Yield: 19.5 g. of a polymer being composed of randomly distributed recurring units of the formulae:

t J11oH2o 0N, 3 1011 804- In p11, me on,

PREPARATION 5 Sulp'honium salt The polymer contained 65 mole percent of units (A). (b) 14.2 g. of the thus modified polyepichlorohydrin and 12.6 g. of dimethyl sulphate were heated for 2 hours at 100 C. under stirring. The reaction mixture was kneaded with ether and dried under vacuum over P The above recurring units (A) were modified into:

onon,o 8H, g, OHaSOF PREPARATION 6 Quaternization of triphenylphosphine g. of polyepichlorohydrin with a molecular weight of 2000 and 52.2 g. of triphenylphosphine were heated on an oil-bath at 140 C. for 19 hours. After cooling, the solid product was finely divided and washed with ether. The precipitate was sucked off and dried in vacuo. Yield: 57 g. of a modified polyepicholrohydrin comprising 60 mole percent of recurring units of the formula:

PREPARATION 7 Quaternization of tributylphosphine 20 g. of polyepichlorohydrin having a molecular weight of 2000 and 40.5 g. of tributylphosphine were heated on an oil-bath at 130 C. for 8 hours. After cooling, two layers formed, from which the upper layer was decanted (it contained :20 g. of unmodified tributylphosphine). The residue was Washed with-ether, dissolved in 200 ml. of dichloroethane and poured in 500 ml. of ether under stirring. The tough precipitate formed is separated and again washed with water, whereafter it is dried under vacuum over P 0 Yield: 36 g. of a modified polyepichlorohydrin comprising 35 mole percent of recurring units of the formula:

PREPARATION 8 Quaternization of quinoline 20 g. of polyepichlorohydrin having a molecular weight of 2000 and 26 g. of quinoline were heated for 24 hours at C. on an oil-bath. The tough mass formed was dissolved in 250 ml. of water, washed with ether, filtrated and dried by evaporation. Yield: 42 g. of a modified polyepichlor-ohydrin comprising 40 mole percent of recurring units of the formula:

Owing to their excellent electroconductive properties, the modified polyepichlorohydrins of the invention cannot only be used as electroconductive layers in electrographic recording elements, but also as antistatic layers in photographic light-sensitive silver halide materials.

In the following examples the use of the electroconductive materials of the invention is described with relation to electrographic materials. They may be used in all kinds of electrographic processes wherein an electroconductive layer is needed. A survey of these different processes has been given by C. I. Claus in Phot. Sci. and Eng. 7 (1963) pages 5-13. The electroconductive polymeric materials may be used in combination with coatings of various inorganic as well as organic photoconductive substances such as those described in the Belgian patent specification 587,300, the United Kingdom patent specifications 964,871, 964,873, 964,874, 964,875, 964,876,

964,877, 964,879, 970,937, 980,879 and 980,880, and in the German patent specification 1,058,836 and in the Canadian patent specification 568,707. These photoconductive substances may be combined with insulating binder agents, known among others from the U.S. patent specifications 2,197,552, 2,297,691, 2,485,589, 2,551,582 and 2,599,542, from the United Kingdom patent specifications 566,278, 693,112 and 700,502, and from the Belgian patent specification 612,102.

The following examples illustrate the present invention.

EXAMPLE 1 Various tertiary amines were quaternized with different polyepichlorohydrins, as described above. A 10% aqueous solution of each product was then applied to a glass plate and dried. The surface resistance of the resulting layers was measured at different degrees of relative humidity (RH). The results are listed in the following table.

According to Preparation a ternary polyepichlorohydrin sulphonium salt was manufactured. A aqueous solution of this salt was applied to a glass plate, dried, and conditioned at different degrees of relative humidity. The surface resistance at these relative humidities was as follows? Relative humidity in percent 12 17 22 40 50 Surface resistance in 10 ohm/sq. cm 10 1. 1 0. 5 0. 14 0.03

EXAMPLE 3 10% aqueous solutions of the polyepichlorohydrins modified according to Preparations 6, 7, and 8, were coated on glass plates, dried, conditioned at different relative humidities and the surface resistance of the layers formed were measured. The following results were found:

Surface Relative resistance humidity, in 10 Qnaternized amine or phosphinc percent ohm/sq. cm.

Quinoline g Triphcnylphosphine 00 10 .10 1. 5 Tribntylphosphine 52 28 40 EXAMPLE 4 Morpholine was quaternized with polyepichlorohydrins of different molecular weight according to the method described in Preparation 4. From the polymeric quaternary ammonium salts obtained 10% aqueous solutions were coated on glass plates, dried, and conditioned at different relative humidities as indicated in the following table. The surface resistances of the layers were measured. The following results were found:

Recurring Surface units modi- Relative resistance Molecular weight of fied, mole humidity, 10 ohm/ polyepichlorohydrin percent percent sq. cm.

EXAMPLE 5 1.5 g. of polymeric quaternary ammonium salt of polyepichlorohydrin and pyridine formed according to Preparation 1 was dissolved with 0.1 g. of saponin in 100 ml. of water. This solution was applied to a paper support at a ratio of 0.75 to 1 g./sq.crn. After drying, a photoconductive recording layer containing photoconductive zinc oxide grains dispersed in an electrically insulating alkyd resin was applied thereto.

The ratio by weight of zinc oxide to alkyd resin was approximately 5 to l. The amount of coating deposited was such that about 20 g. of zinc oxide was present per sq. m. After drying, the resulting electrophotographic image recording element was tested as follows. The photo conductive layer was charged to about 400 volts by using a negative corona discharge and it wa sthen exposed for 15 see. through a piece of letterpress type to a radiation of 2280 lux from a 450 watt incadescent lamp.

A developing powder, made according to known manufacturing methods from a copolymer of styrene and butyl methacrylate (70:30 mole percent, polyvinyl butyral and carbon black in a ratio by weight of 8011218 respectively, was then dusted over the sheet and attracted by the charged portions of the paper, so as to produce thereon a patterned image of the letterpress type. By heating, the developing powder was fused and a sharp, permanent image was formed.

EXAMPLE 6 The process of Example 5 was repeated but the inorganic photoconductive zinc oxide was replaced by an organic photoconductive material viz polyvinylcarbazole. The photoconductive coating composition contained 5% by weight of polyvinyl carbazole and as binder 5% by weight of a copolymer of vinyl chloride, vinyl acetate and maleic anhydride (:142l). Methylene chloride was used as solvent. The amount deposited was such that after drying 2 g. of polyvinylcarbazole was present per sq. m.

After charging and exposing through a piece of letterpress type as in Example 5, the patterned image on the electrophotographic image-recording element was developed by means of an electrophoretic developing composition such as described in Example 11 of published Dutch patent application 6701696.

A sharp, permanent image of the original was obtained.

EXAMPLE 7 1.5 g. of polymeric quaternary ammonium salt of polyepichlorhydri-n and pyridine formed according to Preparation 1 was dissolved in a mixture of 20 ml. of water and 80 ml. of ethanol and coated on a paper support at a ratio of 0.75 to l g./sq. m. A photoconductive layer was applied thereto as described in Example 5. The resulting electrophotographic image-recording ele ment was tested as described in the same example. A sharp very contrasty image was obtained.

EXAMPLE 8 1.5 g. of polymeric quaternary ammonium salt according to Preparation 1, 0.1 g. of saponic, 2.5 g. of gellatin, and 0.2 g. of formaldehyde were dissolved in ml. of water and coated on a paper support at a ratio of 0.75 to l g./sq. m. The further procedure of Example 5 was then followed. A sharp, very contrasty image was produced.

EXAMPLES 9 TO 11 The process of Examples 5, 7 and 8 was repeated, with the proviso, however, that instead of paper a film of cellulose triacetate was used as support and that the electroconductive solution was applied to a ratio of only 0.5 g./sq.m. In all three cases an electrophotographic image-recording element yielding very good contrasty images was produced.

EXAMPLE 12 1.5 g. of polymeric quaternary ammonium salt of polyepichlorohydrin and pyridine formed according to Preparation 1 was dessolved with 0.1 g. of saponin in 100 ml. of water. This solution was applied to a paper support at a ratio of 0.75 to 1 g./sq. 111. After drying, an insulating layer of polyvinyl acetate (about 5 g./sq.m.) was applied thereto.

An original of a drawing was scanned by means of a flying spot scanner, so that the recorded information modulated an electron beam in a cathode ray tube. The modulated electron beam was directed against a row of magnetic wires in the tubes front plate.

The electrographic image recording element consisting of the paper support, the electroconductive layer of polymeric material and the insulating layer as indicated above, was held against the front plate of the tube. The electron beam is accelerated by applying a voltage between the electroconductive layer and the cathode ray tube. In this way the sensitivity and the density were increased.

The charge image formed on the insulating layer was rendered visible by means of an electrophoretic developing composition as described in Example 3 of published Dutch patent application 6701696.

After evaporation from the recording layer of the solvent of the electrophoretic developing composition an measureproof image of the original drawing was obtained.

What we claim is:

1. An electrophotographic recording element comprising a support, a film formed of an electroconductive polymeric material composed of randomly distributed recurring units of the formulae:

cm-oH -o and on-en o l J 1 J wherein the ratio of recurring units (A) may vary between about 25 and 95 mole percent of the total amount of units (A) and (B) present and wherein R is a quaternary ammonium, phosphonium, or tertiary sulfonium group and X is an anion and .a photoconductive layer coated upon said film. 1

2. An electrographic recording element according to claim 1, wherein R is a trialkylammonium group, a tri- (hydroxyalkyD-ammonium group, a N-alkyl-di(hydroxyalkyl)-ammonium group, an alicyclic ammonium group, a triarylammonium' group, a N-dialkyl-arakylammonium group, or an heterocyclic ammonium group, the various 10 alkyl groups of which are branched or straight chain alkyl groups of 1 to 4 carbon atoms.

3. An electrographic recording element according to claim 1, wherein R is a pyridinium group.

4. An electrographic recording element according to claim 1, wherein R is a morpholinium group.

5. An electrographic recording element according to claim 1, wherein the R is selected from a trialkyl-phosphonium group and a triarylphosphonium group, the alkyl groups therein being branched or straight chain alkyl groups of 1 to 4 carbon atoms.

6. An electrographic recording element according to claim 1, wherein the R is selected from a dialkylsulphonium group, a S-alkyl-hydroxyalkylsulphonium group, a di(hydroxyalkyD-sulphonium group, a S-alkyl-carboxyalkylsulphonium group, a S-alkyl-carboxyalkoxyalkylsulphonium group, a diarylsulphonium group, a S-alkyl aralkyl-sulphonium group, and a di(alkoxy-alkyl)sulphonium group, the various alkyl groups of which are branched or straight chain alkyl groups of 1 to 4 carbon atoms.

7. An electrographic recording element according to claim 6, wherein the R is S-methyl-hydroxy-ethyl-sulphonium.

8. An electrographic recording element according to claim 1, wherein the anion is selected from a halide and methylsulphate.

References Cited UNITED STATES PATENTS 3,011,918 12/1961 Silvernail et a1 96-l.5 X 3,216,853 11/1965 Gess ll72l8 X 3,248,279 4/1966 Geyer 117201 X 3,293,115 12/1966 Lucken 117-201 X 3,479,215 11/1969 Savagna et a1. 162l38 X 3,275,573 9/1966 Vanderberg 260-2 EPA 3,403,114 9/1968 Vandenberg 260-2 EPA GEORGE F. LESMES, Primary Examiner J. R. MILLER, Assistant Examiner US. Cl. X.R.

96-87 A; ll72l8, 161 ZB; 162-138; 2602 A, 79 

